Re: [BUG] io_uring: defer logic based on shared data

From: Jens Axboe
Date: Fri Oct 25 2019 - 12:27:57 EST

On 10/25/19 10:21 AM, Pavel Begunkov wrote:
> On 25/10/2019 19:03, Jens Axboe wrote:
>> On 10/25/19 3:55 AM, Pavel Begunkov wrote:
>>> I found 2 problems with __io_sequence_defer().
>>> 1. it uses @sq_dropped, but doesn't consider @cq_overflow
>>> 2. @sq_dropped and @cq_overflow are write-shared with userspace, so
>>> it can be maliciously changed.
>>> see sent liburing test (test/defer *_hung()), which left an unkillable
>>> process for me
>> OK, how about the below. I'll split this in two, as it's really two
>> separate fixes.
> cached_sq_dropped is good, but I was concerned about cached_cq_overflow.
> io_cqring_fill_event() can be called in async, so shouldn't we do some
> synchronisation then?

We should probably make it an atomic just to be on the safe side, I'll
update the series.

Jens Axboe